Mechanism of oxygen reduction by metallocenes near liquid|liquid interfaces

T. Jane Stockmann, Haiqiang Deng, Pekka Peljo, Kyösti Kontturi, Marcin Opallo, Hubert H. Girault*

*Corresponding author for this work

    Research output: Contribution to journalArticleScientificpeer-review

    13 Citations (Scopus)

    Abstract

    The mechanism of the oxygen reduction reaction (ORR) at a liquid|liquid interface, employing ferrocene (Fc) derivatives - such as decamethylferrocene (DMFc) - as a lipophilic electron donor along with sulfuric acid as an aqueous proton source, was elucidated through comparison of experimentally obtained cyclic voltammograms (CVs) to simulated CVs generated through COMSOL Multiphysics software which employs the finite element method (FEM). The simulations incorporated a potential dependent proton transfer (i.e. ion transfer, IT) step from the water (w) to organic (o) phases along with two homogeneous reactions (C1C2) occurring in the organic phase - an IT-C1C2 mechanism. The reaction of DMFc with H+(o) to form DMFc-hydride (DMFc-H+) was considered the first step (reaction 1), while reaction of DMFc-H+ with oxygen to form a peroxyl radical species, HO2, and DMFc+ was deemed the second step (reaction 2). Subsequent reactions, between HO2 and either DMFc or H +, were considered to be fast and irreversible so that 2 was a 'proton-sink', such that further reactions were not included; in this way, the simulation was greatly simplified. The rate of 1, kcf, and 2, k chem, were determined to be 5 × 102 and 1 × 104 L mol-1 s-1, respectively, for DMFc as the electron donor. Similarly, the rates of biphasic ORR for 1,1′- dimethylferrocene (DFc) and Fc were considered equivalent in terms of this reaction mechanism; therefore, their rates were determined to be 1 × 102 and 5 × 102 L mol-1 s-1 for 1 and 2, respectively. The reactive and diffusive layer thicknesses are also discussed.

    Original languageEnglish
    Pages (from-to)43-52
    Number of pages10
    JournalJournal of Electroanalytical Chemistry
    Volume729
    DOIs
    Publication statusPublished - 1 Sep 2014
    MoE publication typeA1 Journal article-refereed

    Keywords

    • 1,1′-Dimethylferrocene
    • COMSOL
    • Decamethylferrocene
    • Ferrocene
    • Liquid|liquid interface
    • Oxygen reduction reaction

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